This application claims the priority of the Swiss applications 0871/00 and 1160/00, filed May 4 and Jun. 13 2002, respectively, and the disclosure of which is incorporated herein by reference in its entirety.
The invention relates to a flow sensor for a liquid as well as to a method for its production.
It has been known to measure the flow velocity and the mass flow, respectively, of a fluid with a semiconductor device, on which a heat source and at least one temperature sensor are arranged. The flow leads to a change of the temperature distribution of the heat source, which can be measured by means of the temperature sensor or temperature sensors.
Semiconductor devices of this type are, however, sensitive. In contact with liquids, an undesired diffusion of substances affecting the properties of the device occurs easily. Furthermore, mechanical strain can damage the device. Hence, the semiconductor devices have to be protected in complicated manner, e.g. by protection layers.
Hence it is an object to provide a flow sensor of the type mentioned initially that can measure a plurality of different liquids, that is robust and that can be manufactures easily.
This object is achieved by the flow sensor of the invention.
Hence, according to the invention the semiconductor device is arranged on an exterior side of a tube section, namely in such a manner that it is in thermal contact with this exterior side. Surprisingly it has been found that such an arrangement still allows accurate and sensitive measurements. As the liquid is guided in the tube section and does not come into contact with the semiconductor device and its passivation layers, respectively, damages can be avoided.
The semiconductor device can e.g. be in direct thermal contact with the exterior side of the tube, or it can be connected thereto via heat conducting elements, e.g. of a metal. It is also possible to arrange an adhesive layer, e.g. of a solder, between the tube section and the semiconductor device, or thermally conducting paste can be used.
The tube section can e.g. be of glass or metal, wherein metal is preferred because of its high thermal conductivity. Other materials, such as plastic, can, however, also be used.
The tube section can be made of a single part or of several individual tube parts.
In order to guarantee a better heat contact, the exterior side of the tube can also be designed to be flattened in the region of the semiconductor device and/or the tube can have a thinned wall region.